The present invention relates to syringes and, more particularly, to a hand-held pneumatic power assisted syringe for injection of fluid.
One application of the present invention is the injection of contrast media through small-diameter angiographic catheters and the invention will be described with particular reference thereto. It is to be appreciated, however, that the invention may be employed for other purposes such as the injection of thrombolytic drugs through small diameter infusion catheters. The invention may also be employed for auto-perfusion of a patient's blood through the distal lumen of a balloon dilatation catheter during balloon inflation to reduce ischemia. The invention may also be employed for inflating angioplasty and valvuloplasty dilatation balloons. Another application may include the injection of contrast media through the distal lumen of balloon dilatation catheters to visualize the distal vessels in angioplasty. Another application may be the injection of contrast media through the guiding catheter in an angioplasty procedure with the balloon dilatation catheter in place. Another application may be the injection or infusion of other drugs and medications, such an anti-tumor drugs through small infusion catheters.
In angiography, for example, a catheter is placed in an appropriate blood vessel and advanced to the site within the circulatory system to be studied. A radio opaque contrast media is injected through the catheter and flows to the distal end of the catheter into the blood vessel. The area within the blood vessel containing the contrast media can be visualized by means of fluoroscopy. The flow rate from the catheter must be equal to or greater than the rate of blood flow within the blood vessel to obtain good opacification. The flow rate from the catheter is dependent upon the pressure exerted upon the proximal end of the catheter, the length of the catheter, the inner diameter of the catheter, and the viscosity of the contrast media to be injected into the blood vessel.
Small diameter catheters are required for entering small vessels or when blood vessels have a tortuous path. Because of the length and small inner diameters of these catheters, difficulties have been encountered in obtaining the pressure needed to produce the flow rate required for good opacification of the area of the blood under investigation. Frequently, the desired flow rate cannot be attained by manual injection as with a typical manually operated syringe.
The present invention provides a hand-held power assisted syringe which may generate sufficient pressure to inject a contrast media or the like through such a catheter to obtain a flow rate which permits good opacification of the vessel being studied.
The U.S. Pat. No. 3,605,745 to M. Hodosh discloses a hydraulic-powered injection system which includes separate pneumatic-hydraulic cylinders which transfer gas pressure to hydraulic pressure to actuate the piston of a syringe. Hodosh does not include a manual control system built into the syringe so that the gas pressure works as an assist to the manual operation of the syringe. Moreover, the device in Hodosh includes a chamber between the drive-fluid chamber and the injectate chamber. The chamber does not communicate with the atmosphere and, hence, is subject to leakage conditions.
The U.S. Pat. No. 4,323,066 to F. Bourdon discloses a manually controlled hydraulic fluid operated syringe for injection of fluids. Bourdon's device operates by having gas pressure balanced on both sides of a piston until the operator pushes on an operating handle. At that time, the gas flow is shut off where it passes through the piston, causing the downstream pressure to drain down to zero through a vent hole. As the downstream pressure bleeds down below the upstream pressure, the piston is driven forward. In this device, gas pressure is being employed even when the piston is not being actuated. Moreover, there is no venting of the gas pressure downstream of the piston for safety purposes. Consequently, a device such as employed by Bourdon can only be used for relatively low gas pressure for power assistance.